The inventor of the present invention and others have proposed a technology of a recording/reproducing apparatus using SNDM (Scanning Nonlinear Dielectric Microscopy) for nanoscale analysis of a dielectric recording medium. In the SNDM, by using an electrically conductive cantilever (or probe) having a small projection on its tip, which is used for atomic force microscopy (AFM) or the like, the resolution of measurement can be increased to sub-nanometer. Recently, by applying the technology of SNDM, a super high-density recording/reproducing apparatus has been developed, wherein the apparatus records data into a recording medium having a recording layer made of a ferroelectric material (refer to a patent document 1).
On the recording/reproducing apparatus using such SNDM, the information is reproduced by detecting the positive/negative direction of polarization of the recording medium. This is performed by using the fact that the oscillation frequency of a LC oscillator, which includes a high-frequency feedback amplifier including a L component, the electrically conductive probe mounted on the amplifier, and the capacitance Cs of a ferroelectric material under the probe, is changed by a change ΔC in small capacitance, which is caused by the extent of a non-linear dielectric constant due to the distribution of the positive/negative polarization. Namely, this is performed by detecting a change in the distribution of the positive/negative polarization, as a change in oscillation frequency Δf.
Moreover, in order to detect the difference in the positive/negative polarization, an alternating electric field having sufficiently low frequency with respect to the oscillation frequency is applied to the oscillation frequency, to thereby change the oscillation frequency with the alternating electric field. At the same time, a ratio of the change in the oscillation frequency, including a code or sign, is determined from the non-linear dielectric constant of the ferroelectric material under the probe. Moreover, by extracting a component caused by the alternating electric field by using the FM (Frequency Modulation)-demodulating, from a high-frequency signal of the LC oscillator, which is FM-modulated in accordance with the change ΔC in the small capacitance associated with the application of the alternating electric field, the record information recorded in the ferroelectric recording medium is reproduced.
Patent document 1: Japanese Patent Application Laying Open NO. 2003-085969